Isolation device for shock reduction in a neonatal transport apparatus

ABSTRACT

A device in combination with a neonatal transport cart that reduces the amount of energy transmitted to the surface upon which an infant rests during transport. A pair of plates, one of which is mounted to the incubator and the other of which is mounted to the stretcher, has a gap between the substantially parallel plates. The gap contains springs, preferably gas springs, with a spring rate in a range and a damping effect. The springs reduce the energy transmission to the infant by the stretcher or other platform.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to mechanisms for transporting newborninfants by ground or air transportation.

2. Description of the Related Art

Neonatal transport is the transport of newborn infants to a medicalfacility to provide critical care. Transportation is typicallyaccomplished via ground, such as by ambulance, and air, such as byairplane or helicopter. The transportation of neonatal patients byconventional means, such as in neonatal transport systems attached tomedical stretchers in ambulances, exposes the patients to physical shockand vibration communicated through the relatively rigid structures, andthis shock is often detrimental to the medical condition of the patient.Current neonatal transport systems do not include an effective subsystemfor shock suppression.

Neonatal patients often exhibit extreme sensitivity to external stimuliincluding physical manipulation. The result of external stimuli is oftenmanifested by a change in heart rate or breathing rate ultimatelyaffecting the oxygenation rate (% oxygen) in the bloodstream.

Poor rear suspension with a narrow wheel base and high center ofgravity, as well as poor road conditions, can lead to uncomfortablebouncing of a medical stretcher. This may be detrimental to somepatients, especially those with orthopedic injuries. Relating to airtransport, gravitational forces can lead to variations in cardiacoutput, and the shifting of a patient due to motion or vibration couldbe disastrous for one who has a cervical spine injury. Vibration andnoise can be disconcerting to the patient, lead to increased anxiety,and be manifested physiologically by increased blood pressure, heartrate, diaphoresis, and combativeness.

Transportation can increase the stress of the infant. Some conditionsmay worsen during transport due to the vibrations and bumps of the ride,and chest tubes may move and get dislodged with the movement orvibrations of the ambulance. Noise and vibration have a greater effecton neonates, and medical equipment can also be adversely affected.

Despite the adverse effects of transportation on neonatal patients,there has been little advancement in this field. The existing neonataltransport cart is an adult stretcher with approximately 450 pounds ofinstrumentation and equipment mounted on the support platform, asillustrated in FIG. 1. The neonatal equipment includes an incubator(also referred to as an isolette), temperature monitoring instruments,and vital sign indicators. In all, the value of this system is oftenclose to $500,000. Transport teams utilize these carts for movingcritical patients. Accelerations experienced in a typical transportsystem can be as high as 2.5 g.

The prior art does not contain a suitable solution for the problem ofthe transmission of shock and vibration to neonatal patients. The needexists for a system to reduce the transmission of kinetic energy toneonatal patients.

BRIEF SUMMARY OF THE INVENTION

The invention is an apparatus for reducing the transmission of kineticenergy from a support platform to an incubator upon which an infant isresting. The apparatus comprises a first plate mounted to the supporttable and a second plate spaced from the first plate to form a gap. In apreferred embodiment, the first plate is substantially parallel to thesecond plate and the second plate is mounted to the incubator. At leastone spring is mounted in the gap between the first and second plates,the spring further comprises a plurality of gas springs mounted in thegap, and each of said springs is mounted to the plates.

In a more preferred embodiment, some gas springs are mounted to theplates in a reverse configuration to prevent damage to other of saidsprings. This reverse configuration prevents the gas springs from beingdamaged under tensile force.

The invention is a shock suppression system designed to fit between theisolette and the stretcher platform. This location facilitates the useof an existing quick disconnect mechanism and minimizes the ergonomicimplications on the transport team personnel.

An air spring based system is disclosed in which air springs are mountedbetween a pair of stiff plates. One plate is for mounting to theisolette, and the other plate is for mounting to the support platform,such as a stretcher. The system dynamics show that effective attenuationof the vibrations can be achieved by the air springs. The effect ofincreasing pressure in the air springs is presented. Furthermore, thepressure in the air springs and the configuration of the air springsaffect the transport cart system response at low frequencies. Therefore,the dynamic model of the transport cart is a valuable tool in theprocess for redesign of the neonatal transport cart.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a side view in perspective illustrating a conventionalneonatal transport cart and isolette.

FIG. 2 is a side view illustrating the preferred embodiment of thepresent invention in an operable position on a transport cart.

FIG. 3 is a table containing air spring stiffness equation parameters.

FIG. 4 is a table containing nominal system parameters.

FIG. 5 is a schematic illustration of a neonatal transport cart incombination with the vibration absorber of the present invention.

In describing the preferred embodiment of the invention which isillustrated in the drawings, specific terminology will be resorted tofor the sake of clarity. However, it is not intended that the inventionbe limited to the specific term so selected and it is to be understoodthat each specific term includes all technical equivalents which operatein a similar manner to accomplish a similar purpose. For example, theword connected or term similar thereto are often used. They are notlimited to direct connection, but include connection through otherelements where such connection is recognized as being equivalent bythose skilled in the art.

DETAILED DESCRIPTION OF THE INVENTION

U.S. Provisional Application No. 60/721,630 filed Sep. 29, 2005 isincorporated herein by reference.

The preferred embodiment of the present invention is shown in FIG. 2.The invention includes a pair of plates 10 and 12 arranged in asubstantially parallel relationship. The plates 10 and 12 are preferablysheet metal, such as stainless steel, but could be aluminum, wood,composite or any other suitable material in sheet form. The upper plate10 mounts, in an operable position, to the underside of the isolette 8(see FIG. 1). The lower plate 12 mounts, in an operable position, to theupper surface of the neonatal transport cart 40, shown in FIG. 2. Theplates 10 and 12 can mount to the respective structures using screws,adhesives, specialized brackets that clamp or any other conventionalfastener. Furthermore, the transport cart 40 is but one of many types ofsupport platforms upon which the invention can be mounted. Otherconventional supports can be used in combination with the invention. Theconventional structures operate in a conventional manner, except for theeffect of the invention, as will be described below.

The plates 10 and 12 are separated by a gap, and at least one air springis interposed in that gap, with firm attachment to each of the plates 10and 12. It is preferred that multiple air springs mount to the plates 10and 12 in the gap, and it is most preferred that nine air springs aremounted in the gap, with two at each corner of the rectangular plates 10and 12, and one in the center. However, the number of air springs mustbe at least one, and there is no theoretical upper limit to the numberof air springs. Of course, because of the cost of air springs, therewill be a practical upper limit to the number.

The air springs 20, 22, 24, 26 and 28 mount at their upper ends to theupper plate 10 using a screw-threaded shaft extending upwardly throughan opening in the plate 10 and a nut fastened on the opposite side ofthe plate 10. The air springs 20-28 mount at their lower ends to thelower plate 12 using similar fasteners. The air springs 20, 22, 26 and28 are mounted at the four corners of the rectangular plates 10 and 12,and the spring 24 mounts centrally of the plates 10 and 12 by fasteningto the plates 10 and 12 in a manner similar to the springs positioned atthe peripheral edges of the plates.

Each of the corner air springs 20, 22, 26 and 28 is a conventionalspring, such as, for example, a Firestone Industrial model 2M2A AirMount. The central air spring 24 can be, for example, a model 16 AirMount. Of course, substitute air springs can be used, as will beunderstood by the person having ordinary skill. Still further, othersprings, whether mechanical, magnetic, elastomeric or any other type,can be used in place of the air springs 20-28, as will be understood.For example, it is contemplated that mechanical springs in combinationwith dampers, such as dashpots or friction brakes, can be substitutedfor the preferred air springs, with resulting practical effects thatwill be understood by the person having ordinary skill in the art.

The air springs 20-28 are designed to sustain a compressive load appliedby the plates 10 and 12, which tends to bring the plates closer to oneanother. Although not shown in FIG. 2, it is preferred that anadditional air spring be mounted at each corner of the plates 10 and 12in order to protect the springs 20, 22, 26 and 28 under tensile loadsapplied by the plates 10 and 12. These tensile load-protecting springsprevent the springs 20-28 from being pulled apart or otherwise damagedby movement of the plates 10 and 12 away from one another.

The air springs 20-28 have both a spring rate and a measurable degree ofdamping. Thus, the air springs 20-28 provide not only a spreading of theapplication of the force applied through the cart to the isolette over agreater period of time, but they also dampen to reduce the transmissionof energy through the invention. Thus, not all of the energy that isapplied to the cart, such as by the floor of the ambulance in which thecart is riding, is transferred to the isolette. In fact, it is preferredthat a substantial amount of energy is not transferred to the isolette,and this is accomplished by the invention.

The vibration isolation is achieved, in the preferred embodimentdescribed above, using air springs between the stretcher and theisolette. Air springs are preferred for vibration isolation due to theirlow system natural frequencies (less than 5.0 Hz) which can be reducedby use of a reservoir. Further, the system natural frequencies do notchange significantly with a change in load.

The spring rate of an air spring is not constant and is a function ofthe change in effective area, volume, and pressure. This stiffness ofthe air springs is related to two factors: the variation in volume, andthe variation of effective area. This overall stiffness is given as:$F_{s} = {{\frac{{nP}_{1}V_{1}^{n}A}{V_{1}^{n + 1}} \cdot \frac{\mathbb{d}V_{1}}{\mathbb{d}h}} - {\left( {P_{1} - P_{a}} \right)\frac{\mathbb{d}A}{\mathbb{d}h}}}$where F_(s) is the stiffness of the air spring system and the equationparameters are defined in FIG. 3. It is preferred that the stiffness ofthe air spring system range from no less than about 500 lb/in, and nomore than about 4,500 lb/in. The preferred range is about 800 lb/in.

The 4.5 in. diameter spring 24 is positioned at the center of the plates10 and 12 and the four 1.34 in. diameter springs 20, 22, 26 and 28 areplaced at the corners of the plates 10 and 12. The theoretical systemmodel, with reference to the schematic illustration of FIG. 5 and theequation parameters as defined in FIG. 4, is: ${{\begin{bmatrix}M_{1} & 0 \\0 & M_{2}\end{bmatrix}\begin{bmatrix}{\overset{¨}{x}}_{1} \\{\overset{¨}{x}}_{2}\end{bmatrix}} + {\begin{bmatrix}{C_{1} + C_{2}} & {- C_{2}} \\{- C_{2}} & C_{2}\end{bmatrix}\begin{bmatrix}{\overset{.}{x}}_{1} \\{\overset{.}{x}}_{2}\end{bmatrix}} + {\begin{bmatrix}{K_{1} + K_{2}} & {- K_{2}} \\{- K_{2}} & K_{2}\end{bmatrix}\begin{bmatrix}x_{1} \\x_{2}\end{bmatrix}}} = \begin{bmatrix}F \\0\end{bmatrix}$where K₂ is the stiffness of the air spring system. The stiffness of theair spring system is a function of the pressure in the springs as wellas the configuration used. FIG. 5 shows the principle behind theinvention: that the appropriate combination of spring rate and dampingresults in a device that greatly reduces the transmission of energy tothe incubator upon which the infant is resting. Other apparatuses withspring and damping characteristics within the range described herein canbe substituted for the preferred embodiment. For example, the centralair spring can be 11.34 cm in diameter and the outer air springs can be3.4 cm diameter.

The system natural frequency due to the inclusion of air springs wasdetermined to be close to 3 Hz. Effective attenuation of the vibrationswas achieved by the air springs, and “effective attenuation” is definedherein to include a range extending from about 10 Hz to about 18 Hz.Preferably, the system attenuates vibrations in the range of about 10.25to about 17.09 Hz. At frequencies greater than about 10 Hz, theattenuation obtained for the various configurations was similar.However, at lower frequencies the response amplitude was considerablyaffected by the configuration.

The spring system is designed for damping in a range extending from justgreater than zero to about 4.0%. Thus, the invention serves to dampenthe oscillatory motion of the incubator resulting from the shock of thevibratory motion of the transport and to reduce the amount of energytransmitted to the isolette in the manner of a shock absorber. Somedamping occurs due to stretching of the bladder in the air springs20-28, although any shock absorber mechanism preferably has somemeasurable damping.

Because the stiffness of an air spring is a function of the pressure, anincrease in air pressure results in higher stiffness. Thus, onecontemplated alternative is to vary the pressure in the springs duringuse, such as by the conduits 30 and 32 having gas passages therein influid communication with the reservoirs of the springs 20-28. The gaspassages in the conduits 30 and 32 are connected to a pneumatic ram orother pressure increasing and decreasing device (not shown). Bycompressing or expanding the gas through the conduits 30 and 32, thedevice thereby increases or decreases the pressure in the springs 20-28.

The invention was tested in three configurations at an increasedpressure level to ascertain a suitable configuration. The test resultsrevealed the effect of increasing pressure for the three possibleconfigurations. It is expected that as the pressure in the air springsis increased, the amplification of the input at the damped naturalfrequency of the system model increases. Furthermore, an increase in airspring pressure increases the stiffness associated with the spring,which increases the natural frequency. The effective stiffness for eachconfiguration differs due to the contributions of the individual springsand the corresponding pressure.

A configuration that consisted of smaller springs oriented at thecorners of the rectangular plates displayed the greatest effect from anincrease in pressure with a decrease in transmission at low frequencies.The inventor concluded that the absence of the large spring in thecenter explained some of this difference in response.

An air spring based system can effectively attenuate the vibrationsexperienced by the transport cart. Additionally, the air spring pressureand the air spring configuration can affect the system behavior at lowfrequencies. Still further, increased insight into the effect of the airspring pressure on the system response can assist the designer in airspring selection.

It is noted herein that alternative embodiments of the invention exist.It would not be possible to describe all such alternative embodimentsherein. However, it will be understood that circular plates withnumerous springs at the periphery could be substituted for the preferredembodiment shown in FIG. 2. Additionally, oval or triangular platescould be used with springs at positions that will be known by the personhaving ordinary skill from the description herein. The plates can bevirtually any shape as can the arrangement of the springs between theplates.

This detailed description in connection with the drawings is intendedprincipally as a description of the presently preferred embodiments ofthe invention, and is not intended to represent the only form in whichthe present invention may be constructed or utilized. The descriptionsets forth the designs, functions, means, and methods of implementingthe invention in connection with the illustrated embodiments. It is tobe understood, however, that the same or equivalent functions andfeatures may be accomplished by different embodiments that are alsointended to be encompassed within the spirit and scope of the inventionand that various modifications may be adopted without departing from theinvention or scope of the following claims.

1. An apparatus for reducing the transmission of kinetic energy from asupport table to an isolette in which an infant is resting, theapparatus comprising: (a) a first plate mounted to the support table;(b) a second plate spaced from the first plate to form a gap, the secondplate being mounted to the isolette; and (c) at least one spring mountedin the gap between the first and second plates.
 2. The apparatus inaccordance with claim 1, wherein the first plate is substantiallyparallel to the second plate.
 3. The apparatus in accordance with claim1, wherein said at least one spring further comprises a plurality ofsprings mounted in the gap, each of said springs being mounted to atleast one of the plates.
 4. The apparatus in accordance with claim 3,wherein said plurality of springs further comprises a plurality of gassprings mounted around a peripheral edge of the first plate and around aperipheral edge of the second plate.
 5. The apparatus in accordance withclaim 4, further comprising a central gas spring mounted to the firstand second plates and positioned centrally of said plurality of gassprings.
 6. The apparatus in accordance with claim 5, wherein at leastsome of said plurality of gas springs are mounted to the plates in areverse configuration to prevent damage to other of said springs.
 7. Theapparatus in accordance with claim 1, wherein the stiffness of said atleast one spring is in a range from about 500 lb/in and about 4,500lb/in.
 8. The apparatus in accordance with claim 7, wherein thestiffness of said at least one spring is about 800 lb/in.
 9. Theapparatus in accordance with claim 1, wherein an effective attenuationof the apparatus is in a range from about 10 Hz to about 18 Hz.
 10. Theapparatus in accordance with claim 9, wherein the effective attenuationof the apparatus is in a range from about 10.25 to about 17.09 Hz. 11.The apparatus in accordance with claim 1, wherein a damping rate is upto about 4.0%.